1. Field of the Invention
The present invention relates to a method for high-pressure processing which is employed for cleaning an object having projections and depressions on a surface of the object (a microstructured surface), for example, a semiconductor substrate. In particular, the present invention relates to a method for high-pressure processing to optimize a depressurizing step after a high-pressure processing step.
2. Description of the Related Art
In a process for manufacturing a semiconductor, patterning with a resist requires a high-pressure processing including: a cleaning step of removing undesired materials such as an unnecessary resist remaining on a substrate after patterning and contaminants such as a polymeric substance formed during etching and remaining on the substrate; and a step of drying surfaces of the substrate to remove moisture on the surfaces of the substrate.
Since a process for manufacturing a semiconductor is usually performed in a clean room, a high-pressure processing is preferably performed in the clean room. However, since building and maintaining a clean room require considerable expenses, small occupying space and excellent functionality have been required for a high-pressure processing apparatus. The demands are further increasing with finer design rules of a semiconductor.
In recent years, on a process for manufacturing a semiconductor, a method for high-pressure processing with a supercritical fluid has been conducted.
For example, in a cleaning substep of a high-pressure processing step, to enhance the efficiency of cleaning, it is necessary to quickly pressurize a high-pressure processing chamber after an object is placed into the chamber and to quickly depressurize when removing the object from the chamber.
To address these needs, the inventors have already proposed an apparatus for high-pressure processing and a method for high-pressure processing, which can quickly pressurize and depressurize a high-pressure processing chamber, in Japanese Unexamined Patent Application Publication No. 2002-367943.
In high-pressure processing, there are problems in which the temperature in a chamber is decreased to the vapor-liquid phase coexistence region or a region in which a solid is deposited according to an adiabatic expansion during depressurization; hence, particles are produced due to the appearance of the liquid phase, thus reducing yield of the semiconductor wafer. To solve these problems, a slow rate of depressurization is effective. However, a problem arises in that time required for performing high-pressure processing becomes longer.
In the above-described art already proposed by the inventors, the temperature of a high-pressure fluid is increased before a depressurizing step. Therefore, the depressurizing step can be performed passing through a vapor phase. Consequently, the problem with particles due to the appearance of the liquid phase has been overcome. However, in this art, a cost and time required to increase temperature have been impediments to the improvement of productivity. When heating an object to a temperature above a processing temperature is undesirable, the improvement of the art has been required.